Method and apparatus for applying microwaves to measure the moisture content of material

ABSTRACT

Apparatus for ascertaining the mass and/or the moisture content of successive increments of a running rod containing tobacco and/or filter material for tobacco smoke has a resonator housing with a cylindrical internal chamber which is disposed between an inlet and an outlet and wherein the rod is exposed to microwaves. The housing is made of a metallic material having a low thermal expansion coefficient, and its internal surface is lined with gold or another corrosion resistant substance. A protective plastic tube establishes a path for the rod from the inlet, across the chamber and into the outlet of the resonator housing.

CROSS-REFERENCE TO RELATED CASES

This application is a continuation of application Ser. No. 09/447,794filed Nov. 23, 1999 (now U.S. Pat. No. 6,417,676, issued Jul. 9, 2002),which is incorporated herein by reference.

This application claims the priority of German patent application Ser.No. 198 54 550.9 Nov. 26, 1998. The disclosure of the above-referencedGerman patent application, as well as that of each US and foreign patentand patent application mentioned in the specification of the presentapplication, is incorporated herein by reference.

BACKGROUND OF THE INVENTION

The present invention relates to improvements in apparatus forascertaining certain characteristics of substantially rod-shapedcommodities. More specifically, the invention relates to improvements inapparatus which can be utilized to ascertain the mass and/or themoisture content of rod-shaped commodities which are moved lengthwisethrough the internal chamber of a housing wherein successive incrementsof the moving commodities are subjected to the action of microwaves. Thecommodities constitute, or can constitute, rod-shaped products of thetobacco processing industry, for example, rod-like fillers of shreddedtobacco of the type contained in plain or filter cigarettes, cigarillotobacco or cigar tobacco. Furthermore the commodities can constitutewrapped fillers constituting filter material (such as paper and/orcellulose acetate) for tobacco smoke.

Commonly owned published European patent application Serial No.0791 823A2 and the corresponding U. S. Pat. No. 6,163,158 disclose an apparatuswherein a continuous rod (such rod can comprise a filler of shreddedtobacco confined in a tubular envelope of cigarette paper) is caused toadvance through a resonator housing having an internal chamber where therod is subjected to the action of microwaves in order to ascertain themass and/or the moisture content of the filler. The resonator housingconsists of a metallic material. Changes of the characteristics of themicrowaves which have been influenced by the moving rod in the internalchamber of the resonator housing are evaluated by one or more suitablecircuits (such circuit or circuits can also ascertain thecharacteristics of the microwaves when the internal chamber of theresonator housing is empty) for the purpose of ascertaining andfurnishing information pertaining to the mass and/or the moisturecontent of unit lengths of the moving rod.

OBJECTS OF THE INVENTION

An object of the invention is to provide a novel and improved resonatorhousing for use in apparatus of the type disclosed in the publishedEuropean patent application Serial No. 0 791 823 A2.

Another object of the invention is to provide a resonator housing whichcontributes to the accuracy and/or sensitivity of the apparatus.

A further object of the invention is to provide the apparatus with noveland improved apparatus for defining a path for lengthwise movement ofrod-shaped commodities through the internal chamber of the resonatorhousing.

An additional object of the invention is to provide novel and improvedapparatus for maintaining the temperature of the resonator housingwithin an optimum range to ensure highly accurate measurementspertaining to the mass and/or moisture content of successive incrementsof the moving commodity or commodities.

Still another object of the invention is to provide a novel method ofand novel apparatus for prolonging the useful life of the resonatorhousing.

A further object of the invention is to provide a resonator housing thatis not affected or is not appreciably affected by the so-called skineffect which is a factor affecting the measurements carried out byapparatus employing conventional resonator housings.

Another object of the invention is to provide the apparatus with noveland improved materials for preventing corrosion of the internal and/orexternal surface of the resonator housing.

SUMMARY OF THE INVENTION

One feature of the present invention resides in the provision of anapparatus which can be utilized to ascertain the characteristics ofmoving elongated rod-shaped commodities of the tobacco processingindustry by exposure to microwaves. The apparatus comprises a resonatorhousing having an inlet for admission and an outlet for evacuation ofcommodities, and at least a portion of the housing consists of amaterial having a low thermal expansion coefficient. The exposure ofcommodities to microwaves takes place in an internal chamber which isdisposed between the inlet and the outlet of the housing, and suchexposure normally serves to ascertain the mass and/or the moisturecontent of commodities.

The material of the resonator housing can constitute an alloy, e.g., analloy containing approximately 64% of iron and approximately 36% ofnickel.

In the absence of any undertakings to the contrary, the temperature ofthe resonator housing varies or is likely to vary when the apparatus isin use. Therefore, the apparatus preferably further comprises aregulator for regulating the temperature of the housing; the regulatorpreferably maintains the temperature of the housing at least close to apreselected value in actual use of the apparatus. The regulator cancomprise a thermometer which serves to generate signals denoting thetemperature of the housing, and at least one transistor which isdesigned to dissipate (in response to signals from the thermometer) heatat a rate proportional to variations of the temperature of the housing.It is preferred to resort to a preselected value which is higher thanthe temperature of the atmosphere around the housing.

The internal chamber is preferably configurated in such a way that it issymmetrical with reference to the longitudinal axis of the rod-shapedcommodity being moved through the internal chamber from the inlet to andthrough and beyond the outlet of the resonator housing. For example, thehousing can be provided with an at least substantially cylindricalinternal chamber.

The internal chamber can be, and preferably is, bounded at least in partby a corrosion resistant substance. Such substance can constitute aliner which surrounds a portion of or the entire internal chamber. Thesubstance of the liner can contain at least one metal; for example, theliner can contain or can consist of gold. It is advisable to select themetal of the corrosion resistant substance in such a way that the latteris a good conductor of electric current.

It is further advisable to provide the resonator housing with a linerwhich consists of a corrosion resistant material and coats at least aportion of the external surface of the housing. Such external liner cancontain or consist of gold.

The apparatus can be equipped with a protective tube which surrounds apath for the commodities being moved through the housing in a directionfrom the inlet toward the outlet. The protective tube can be made of orit can contain a suitable plastic material, for example, apolyaryletherketone and preferably a polyaryletheretherketone. Inaccordance with a feature of the invention, the protective tube has areceiving portion which is disposed at the inlet of the resonatorhousing and defines a passage which diverges in a direction away fromthe outlet.

The housing can be provided with an extension which surrounds the inletand/or the outlet and serves to oppose issuance or escape of microwavesfrom the internal chamber between the inlet and the outlet of thehousing.

Still further, the housing can comprise a tubular extension which isprovided at the inlet and/or at the outlet, i.e., in the internalchamber, and which defines a portion of the aforementioned path formovement of commodities from the inlet to the outlet.

The apparatus further comprises microwave generator components foradmitting microwaves from the generator into the internal chamber,preferably microwaves having at least two different frequencies, and acircuit having a comparator for comparing a first resonance curve whichis influenced by the commodities in the housing with a second resonancecurve which is not influenced by the commodities in the housing to thusascertain a shift of frequency of the first resonance curve by thecommodities. The circuit can further comprise a comparator for comparingthe amplitudes of the first and second resonance curves for the purposeof ascertaining the extent of damping of the first curve by thecommodities. The aforementioned different frequencies are preferablyassociated with a downwardly sloping flank of a resonance curve.

Another feature of the invention resides in the provision of anapparatus which serves to ascertain the characteristics of movingelongated rod-shaped commodities of the tobacco processing industry byexposure to microwaves. The improved apparatus comprises a metallichousing having an inlet for admission of commodities, an outlet forevacuation of commodities, and an internal chamber disposed between theinlet and the outlet to provide or establish a region for exposure ofcommodities to microwaves in order to ascertain at least one of (a) themass and (b) the moisture content of commodities. The temperature of thehousing is variable when the apparatus is in use, and the apparatusfurther comprises a regulator for regulating the temperature of thehousing while the apparatus is in use. The regulator can be designed,assembled and operated in a manner as already outlined hereinbefore.

A further feature of the invention resides in the provision of anapparatus for ascertaining the characteristics of moving elongatedrod-shaped commodities of the tobacco processing industry by exposure tomicrowaves. The improved apparatus comprises a metallic housing havingan inlet for admission of commodities, an outlet for evacuation ofcommodities and an internal chamber which is disposed between the inletand the outlet to provide a region for exposure of commodities tomicrowaves in order to ascertain the mass and/or the moisture content ofcommodities. The apparatus further comprises a corrosion resistantsubstance which bounds at least a portion of the internal chamber. Theconfiguration, size and material of the corrosion resistant substancecan be selected as already described hereinbefore.

An additional feature of the invention resides in the provision of anapparatus for ascertaining the characteristics of moving elongatedrod-shaped commodities of the tobacco processing industry by exposure tomicrowaves. The apparatus comprises a metallic resonator housing havingan inlet for admission of commodities, an outlet for evacuation ofcommodities and an internal chamber disposed between the inlet and theoutlet to provide a region for exposure of commodities to microwaves tothus ascertain the mass and/or the moisture content of commodities. Theimproved apparatus further comprises a protective tube which surrounds apath for commodities being moved through the housing from the inlet,through the internal chamber and to and beyond the outlet. The materialand the configuration of the protective tube can be selected in a mannerand for the purposes as pointed out hereinbefore.

The novel features which are considered as characteristic of theinvention are set forth in particular in the appended claims. Theimproved apparatus itself, however, both as to its construction and themodes of constructing, assembling and operating the same, together withnumerous additional important and advantageous features and attributesthereof, will be best understood upon perusal of the following detaileddescription of certain presently preferred specific embodiments withreference to the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING

The single FIGURE of the drawing is a fragmentary central longitudinalsectional view of an apparatus which embodies the features of thepresent invention and is utilized to subject a running wrapped filler oftobacco or filter material for tobacco smoke to the action of microwavesto ascertain the mass and/or the moisture content of the filler.

DESCRIPTION OF PREFERRED EMBODIMENTS

The measuring apparatus a portion of which is shown in the drawing is inthe process of ascertaining certain characteristics of an elongatedcommodity 1 which constitutes a continuous cigarette rod having arod-like filler 2 of shredded tobacco and a tubular envelope 3 ofcigarette paper. The apparatus comprises a novel and improved resonatorhousing 4 including a main portion 6 and a cover or lid 8 detachably(such as threadedly) connected to the main portion. The main portion 6is a relatively short cylinder which defines with the cover 8 acylindrical internal chamber 7 having a symmetry axis at leastsubstantially coinciding with the axis of the rod portion passingthrough the resonator housing 4. Such portion of the rod 1 is subjectedto the action of microwaves which are supplied (particularly for thepurpose of ascertaining the mass and/or the moisture content of thefiller 2) by a least one antenna 16.

The cover 8 and its cover external tubular extension 8 a define an inlet21 of the housing 4, and the main portion 6 and its main portionexternal tubular extension 6 a define an outlet 23 of the resonatorhousing 4. The internal chamber 7 is disposed between and communicateswith the inlet 21 as well as with the outlet 23 of the housing. Theexternal tubular extensions 8 a and 6 a are external extensions incontrast to the relatively short internal tubular extensions 8 b, 6 bwhich project into the chamber 7 to surround an elongated protectivetube 13 which defines the actual path for successive increments of thecontinuous cigarette rod 1.

In accordance with a feature of the invention, the housing 4 (i.e., themain portion 6 and the cover 8) consists, at least in part, of ametallic material having a low (preferably very low) thermal expansioncoefficient. For example, the housing 4 can be made of an alloycontaining approximately 64% of iron and approximately 36% of nickel.Other metallic materials having similar thermal expansioncharacteristics can be utilized with equal or similar advantage. Theability of the metallic material of the resonator housing 4 to retainits selected optimum configuration and optimum dimensions contributessignificantly to the accuracy of results of measurements of selectedcharacteristic(s) of the rod-shaped commodities being advanced along thepath defined by the protective tube 13.

The accuracy of measurements by resorting to an apparatus employing theimproved resonator housing 4 is further enhanced by a temperatureregulator for maintaining the temperature of the housing at least closeto a preselected value in actual use of the apparatus. The illustratedtemperature regulator includes a temperature sensor 9 (herinafter calledthermometer) and at least one heating transistor 11 which receivessignals from (i.e., which is controlled by) the thermometer 9. Thetransistor 11 can be of the type known as BUZ 80 distributed by Siemens.Heat which is being dissipated by the transistor 11 is utilized to raisethe temperature of the housing 4 to maintain the temperature at apreselected value, preferably at a temperature which is above thetemperature in the surrounding atmosphere. The temperature sensor 9 andheating transistor 11 have been found to be eminently suitable tomaintain the temperature of the resonator housing 4 at least close to anoptimum constant (preselected) value.

In accordance with a further important feature o f the invention, theinternal surface of the resonator housing 4 is coated with a substance(e.g., in the form of a liner which surrounds the entire internalchamber 7) which reliably prevents or at least minimizes or delayscorrosion of the housing around the internal chamber. At the same time,the liner at the internal surface 12 of the housing is highlysatisfactory conductor of electric current. A metallic material whichsatisfies such requirements (resistance to corrosion and pronouncedconductivity) is gold or another material exhibiting equivalent orsimilar characteristics. For example, a very thin film of gold can bedeposited upon the internal surface 12 by resorting to a suitablevaporizing apparatus. Prevention of corrosion at the internal surface 12of the resonator housing 4 is desirable and advantageous because suchcorrosion could adversely influence the accuracy of measurements beingcarried out regarding one or more selected characteristics of the movingrod 1. Satisfactory conductivity is desirable and advantageous becausethis prevents the development of the highly undesirable skin effect.

It is often preferred to apply a corrosion-resistant liner or film to aportion of or to entire external surface of the resonator housing 4. Forexample, at least a portion of such external surface can be providedwith a thin or extremely thin liner of gold.

An important purpose of the aforementioned protective tube 13 is tomechanically seal the portion of the internal chamber 7 around the tubefrom those increments of the rod 1 which are being advanced through thehousing 4 from the inlet (at the cover external tubular extension 8 a)to the outlet (at the main portion external tubular extension 6 a). Thisat least reduces the likelihood of contamination of the major part ofthe internal chamber 7 by particles of dirt (e.g., tobacco dust) beingentrained by the external surface of the tubular wrapper 3. The presenceof contaminants in the internal chamber 7 could adversely influence theaccuracy of the results of measurements being carried out upon the rod1. It is presently preferred to make the protective tube 13 of asynthetic plastic material, for example, of the polyaryletherketonegroup (PAEK), especially polyaryletheretherketone (PEEK).

The passage 13 a defined by the rod-receiving portion of the protectivetube 13 preferably diverges in a direction counter to the direction(indicated by the arrows 5) of advancement of the rod 1, i.e., in adirection away from the outlet 23 (at the main portion external tubularextension 6 a) of the resonance housing 4. The diverging passage 13 a isdefined by a substantially funnel-shaped portion of the tube 13.

The purpose of the external extensions 6 a, 8 a of the main portion 6and cover 8 of the resonator housing 4 is to prevent uncontrolled escapeof microwaves from the internal chamber 7. The internal tubularextensions 6 b, 8 b (which are much shorter than the external tubularextensions 6 a, 8 a and extend into the chamber 7) serve a similarpurpose. The internal tubular extensions 6 b, 8 b are optional buthighly desirable.

The components for admitting microwaves from a generator (reference canbe had to the aforementioned published European patent applicationSerial No. 0791 823 A2 or U.S. Pat. No. 6,163,158) into the chamber 7include the antenna 16 which extends through an insulator 14 installedin the bottom end wall of the main portion 6 of the resonator housing 4.The components for conveying microwaves from the internal chamber 7 ofthe housing 4 includes an antenna 18 which extends through an insulator17 also installed in the bottom end wall of the main housing portion 6.The evaluating circuit for microwaves issuing from the resonator housing4 at 18 can be of the type disclosed in the commonly owned publishedGerman patent application Serial No. 197 34 978 A1 and in thecorresponding United States patent application. One mode of evaluatingthe microwaves issuing from the internal chamber 7 while the tube 13confines a length of the rod 1 and the microwaves issuing from thehousing 4 while the tube 13 is empty is described in a preceding passageof this specification.

The improved resonator housing is susceptible of numerous additionalmodifications without departing from the spirit of the presentinvention. For example, the aforementioned percentages of iron andnickel in the alloy constituting a presently preferred metallic materialof the housing 4 can depart from those (64% and 36%, respectively)mentioned hereinbefore. All that counts is to ensure that the thermalexpansion coefficient of the resonator housing is sufficiently low toprevent excessive mechanical deformations in response to fluctuations oftemperature in actual use of the apparatus. Excessive mechanicaldeformations are those which can adversely affect the accuracy of themeasurements of certain characteristics of the elongated rod-shaped(including substantially rod-shaped) commodities. With this in mind, thematerial of the housing 4 can contain constituents other than ironand/or nickel, various percentages of iron and/or nickel, and/or iron,nickel and one or more additional elements.

The internal chamber 7 of the housing 4 which is shown in the drawingresembles a cylinder. However, it is equally possible to select anotherconfiguration which is at least substantially symmetrical with referenceto the axis of the rod portion passing through the tube 13. For example,the internal chamber 7 can be replaced with one having a polygonalcross-sectional outline.

The liner or coating applied to the external surface or to the internalsurface 12 of the housing 4 can consist of pure gold or of an alloywhich contains gold. An advantage of pure gold is that a liner whichcoats the internal surface 12 and constitutes an extremely thin (such asvaporized) layer of pure gold suffices to ensure highly satisfactory andlong-lasting resistance to corrosion as well as a highly satisfactorypronounced conductivity.

Without further analysis, the foregoing fully reveals the presentinvention so that others can, by applying current knowledge, readilyadapt it for various applications without omitting features that, fromthe standpoint of prior art, fairly constitute essential characteristicsof the generic and specific aspects of the above outlined contributionto the art of resonator housing for microwaves. Therefore, suchadaptations should and are intended to be comprehended within themeaning and range of equivalence of the appended claims.

1. In an apparatus for ascertaining the characteristics of movingelongated rod-shaped commodities of the tobacco processing industry byexposure to microwaves, the improvement comprising: a metallic housinghaving an inlet for admission and an outlet for evacuation ofcommodities, wherein said housing has an internal chamber between saidinlet and said outlet and said housing comprises an internal tubularextension provided at least at one of said inlet and said outlet, saidinternal tubular extension being disposed in said chamber and defining aportion of a path for movement of commodities from said inlet to saidoutlet.